The integral measurement is the most common form of exposure measurement (full-field exposure measurement), in which the entire photographic image field is used for exposure measurement.
The integral measurement is used with single-lens reflex cameras , with viewfinder cameras with integrated exposure meters as well as with hand exposure meters . Also working flash units with their own sensor with integral metering.
The light intensity is measured over the entire surface assuming a standardized gray tone that would reflect exactly 18 percent of the light falling on it. In practice, this method in its pure form often leads to incorrect exposures , especially with high subject contrasts , as the bright sky is overestimated in landscape shots , for example, or the actual subject is incorrectly assessed in portraits with a very bright or very dark environment.
Since the important subjects are often in the center of the picture, center-weighted integral measurement was established very early on , in which a more or less large area of the image section in the center is rated more strongly than the image areas between the center and the edges. This will provide correct exposure measurement based on the subject under most circumstances.
DSLR camera manufacturers have developed various refinements to center-weighted integral metering. For example, the different ratings for the Olympus OM-2 are implemented using a pattern printed on the first shutter curtain . With this system, a measuring cell located in the mirror box records the light reflected by the shutter curtain after the lens aperture is closed and thus controls the exposure time. Minolta uses the CLC measurement in the SRT and XE series , in which two measuring cells are arranged in such a way that the measuring ranges overlap in the middle. Many cameras do not use a circular, but rather a trapezoidal measuring surface, in which the lower half of the image in landscape format is considered more than the upper half.
These measures improve the reliability for average subjects, and you get decent results with a large part of the pictures. In unusual lighting conditions, however, the photographer needs some experience with the characteristics of the respective camera model in order to be able to take corrective action.
The main disadvantage of the integral measurement compared to the spot measurement is that the zone measurement method according to Fred Archer cannot be carried out so easily, and the determination of the contrast range of a motif is also very inadequate.
The counterpart to the integral measurement is the selective measurement or spot measurement with concentrated measurement on a very small, defined area without taking the image environment into account. Modern, microprocessor-controlled cameras also offer the matrix measuring method . Some camera models also allow switching between different measurement methods. With digital cameras , apart from very simple models, the option to choose between the various measuring methods is standard today.